1. Field of the Invention
The present invention relates to a mist atomizer and a mist atomizing device for fuel cells. More particularly, the present invention relates to a mist atomizer for atomizing mists, for example to humidify process gases to be supplied to electrodes of a solid polymer fuel cell, and a mist atomizing device for fuel cells using the mist atomizer.
2. Description of Related Art
Conventionally, this type of mist atomizer is used as a humidifier device for process gases supplied to an anode or a cathode of a solid polymer fuel cell (the process gases are a fuel gas in the case of anode and an oxidizing gas in the case of cathode). A solid polymer fuel cell is a type of fuel cell that generates electromotive force (electric energy) by electrochemical reactions in which protons generated from a fuel supplied to the anode transfer to the cathode through an electrolyte membrane and react with an oxidizing gas supplied to the cathode to produce water.
In order to operate the solid polymer fuel cell normally, it is necessary to keep the electrolyte membrane in an appropriate wet state. A general practice to meet this end is to humidify process gases such as a fuel gas supplied to the anode or an oxidizing gas supplied to the cathode by adding mists or steams thereto.
One example of a fuel cell comprising this type of humidifier device using mists is a solid polymer fuel cell disclosed in Japanese Unexamined Patent Publication No. HEI 5-54900. The solid polymer fuel cell comprises a process gas humidifier device for adding mists to a fuel gas or an oxidizing gas by using a mist atomizer having a spray nozzle or an ultrasound atomizer apparatus.
Application of the humidifier device using mists to a fuel cell is advantageous in that mists are transferred as they are to the electrode on the process gases as a carrier, and thus the amount of humidifying water is quantitatively controlled. Further, there is another advantage. That is, the process gases are deprived of latent heat of evaporation when the mists atomize into steams, a cooling effect is expected to take place on the process gases.
On the other hand, one preferred embodiment of this type mist atomizer, an example of which is shown in FIG. 7, is disclosed in Japanese Unexamined Patent Publication No. SHO 57-42362 although its use is not limited to fuel cells. A mist atomizer 70 disclosed in this publication comprises a plurality of (two, in this figure) nozzle heads 74a and 74b spaced uniformly with respect to the central axial line Xxe2x80x94X of a nozzle assembly 72. Each of the nozzle heads 74a and 74b has an air intake conduit 76 and a liquid intake conduit 78 each for introducing pressurized air and liquid respectively. Further, each of the nozzle heads 74a and 74b is provided with a two-fluid nozzle at a particular crossing angle which has a double-pipe construction comprising an air discharge conduit 82 and a liquid discharge conduit 80.
In the case of the mist atomizer disclosed in this publication, pressurized air is supplied through the gas intake conduit 76 accommodated in each of the nozzle heads 74a and 74b. When the pressurized air is atomized from the air discharge conduit 80, liquid supplied through the liquid conduit 78 is sucked into the liquid discharge conduit 82 and atomized therefrom to generate mists. In addition, the mists atomized from each of the nozzle heads 74a and 74b collide with each other at a point of intersection on the central axis line Xxe2x80x94X, and fine mists having particles of ten microns or less are generated through the collision of the jets.
The mist atomizer disclosed in the above-mentioned Japanese Unexamined Patent Publication No. SHO 57-42362 is capable of effectively generating fine mists and of diffusing the mists in the air. However, an order of tens of meters (m) of a spatial extent is required to diffuse the generated mists evenly. In other words, the mist atomizer disclosed in this publication is effective to evenly humidify a wide space such as a room, a factory or a hospital.
On the other hand, in the case of the above-described fuel cell, for the sake of miniaturization of a fuel cell (ensuring its vehicle-mountability) and high power output and high output density of the fuel cell, a gas channel provided in the fuel cell is extremely narrow and inside of the gas channels is a closed space which requires pressure control. In addition, since another components such as a gas supply source are connected by pipes and the like, a sufficient space required to diffuse mists atomized from the two-fluid nozzle can not be secured. For this reason, mere application of the conventional mist atomizer using a two-fluid nozzle to a fuel cell ends up with a problem. That is, since the generated mists are not diffused sufficiently and collide with an inner wall of the channel, the mists are trapped on the wall before being converted into electric power.
In addition, since the utilization efficiency of water supplied to the two-fluid nozzles becomes extremely low, there is a problem that is the need to keep a larger amount of supply water. Further, liquid pools undesirably generated within the channel may be a factor to cause closing of a gas flow (flooding), which hinders stable generation of electric power.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a mist atomizer capable of generating fine mists (about 30 xcexcm or less in diameter) in a stable and continues manner even in a closed space which requires pressure control.
Another object of the present invention is to apply such a high-performance mist atomizer to a humidifier device for maintaining electrolyte membranes of a solid polymer fuel cell in an appropriate wet state so as to provide a mist atomizing device for fuel cells which can achieve stable performance of the fuel cell.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, a mist atomizer comprises a plurality of two-fluid nozzles arranged so that mists atomized therefrom collide with each other, and a secondary gas intake conduit for supplying a secondary gas toward a collision point of the mists.
In addition, it is preferred that the mist atomizer of the present invention further comprises flow control means for preventing the secondary gas from interfering with collision of the mists, and for promoting fine mists generated by the collision to mix with the secondary gas. Also, it is preferred that the mist atomizer further comprises a secondary nozzle disposed at a downstream end of the secondary gas intake conduit for promoting the fine mists generated by the collision of the mists to mix with the secondary gas, and for reducing a cross sectional spray area of the secondary gas.
According to the mist atomizer of the present invention having a construction as above, mists atomized from each two-fluid nozzle collide with each other at a point within the secondary gas intake conduit, thereby generating fine mists. In addition, since the secondary gas is supplied toward the collision point of the mists, the fine mists generated by the collision are accelerated by the secondary gas and promoted to mix with the secondary gas. Also, by provision of flow control means in the secondary gas intake conduit, the secondary gas is prevented from interfering with the collision of the mists atomized from each two-fluid nozzle, and the thus generated fine mists are promoted to mix with the secondary gas. Further, if the secondary nozzle is disposed at the tip of the secondary gas intake conduit, the flow of the secondary gas including the fine mists is restricted its width by the secondary nozzle upon being atomized therefrom.
Accordingly, this mist atomizer is capable generating fine mists (about 30 xcexcm or less in diameter) in a stable and continuous manner even in a closed space where pressure control is necessary. Further, since two-fluid nozzles are applied to this mist atomizer, pressure loss can be kept low and fine mists can be generated from a small amount of supply of gas. Still further, since the fine mists are sufficiently mixed with the secondary gas in a small area and the cross sectional spray area when atomizing the fine mists is made small, it is possible to supply the fine mists into a narrow channel of the fuel cell.
In another aspect of the present invention, a mist atomizing device for fuel cells according to the present invention which humidifies a process gas to be supplied to a fuel cell using mists, the device comprises a mist atomizer, separating means for separating coarse droplets included in the process gas discharged from the mist atomizer, and water supplying means for supplying water to the two-fluid nozzles The mist atomizer comprises a plurality of two-fluid nozzles arranged so that mists atomized therefrom collide with each other and a secondary gas intake conduit for supplying a secondary gas toward a collision point of the mists.
In this case, it is preferred that the mist atomizer further comprises flow control means for preventing the process gas from interfering with collision of the mists, and for promoting fine mists generated by the collision to mix with the process gas. In addition, it is preferred that the mist atomizer further comprises a secondary nozzle disposed at a downstream end of the secondary gas intake conduit for promoting the fine mists generated by the collision of the mists to mix with the process gas, and for reducing a cross sectional spray area of the process gas.
Further, it is preferred that the water supplying means is a supply water tank for collecting the droplets separated by the separating means. In addition, it is preferred that the supply water tank is disposed internally of the fuel cell, and the separating means is a communicating hole which connects a lower tip of the mist atomizer to the supply water tank. Alternatively, it is preferred that the supply water tank is disposed externally of the fuel cell, and the separating means is a collecting conduit which connects a lower tip of the mist atomizer to the supply water tank. In addition, it is preferred that the mist atomizing device for fuel cells according to the present invention further comprising a circulating conduit for supplying the water which has been collected in the supply water tank to the two-fluid nozzles.
Further, it is preferred that the mist atomizing device for fuel cells according to the present invention further comprises a main gas conduit for supplying the process gas to the secondary gas intake conduit, and a branch gas conduit which is branched off from the main gas conduit for supplying part of the process gas to the two-fluid nozzles. In this case, it is preferred that the mist atomizing device for fuel cells further comprising a reflux gas conduit for introducing the process gas running through the branch gas conduit back into the main gas conduit, and a selector valve disposed at a joint portion of the reflux gas conduit and the branch gas conduit for letting the process gas running through the branch gas conduit into one selected from the two-fluid nozzles and the main gas conduit.
According to this mist atomizing device for fuel cells, since the mist atomizer adds fine mists to the process gas, the fine mists flow smoothly through a complicated channel of the fuel cell despite its abrupt enlargement and reduction in diameter and curves. Accordingly, collision of the fine mists with the wall and adherence of the fine mists to the wall are suppressed so that the fine mists are prevented from adhering to the wall. As the result, the fine mists can be distributed into each cell evenly so as to keep electrolyte membranes in an appropriate wet state through the anode or the cathode so that a stable performance of the fuel cell is ensured.
Further, if coarse droplets undesirably generated due to adherence of the fine mists with one another are separated from the process gas to be collected into the supply water tank and if the collected water is supplied to the two-fluid nozzles, the collected liquid water is reused and therefore, a total amount of water that is required to be held in order to humidify a fuel cell is reduced. Here, in order to humidify the fuel cell using a two-fluid nozzle stably, it is required that pressure within the supply water tank and pressure within an spray field of the two fluid nozzle be even. The mist atomizing device for fuel cells according to the present invention satisfies this requirement for pressure control because the circulating conduit is provided to connect the spray field and the supply water tank.